Operating Instructions UVD 170S/340S
12
4.3.5
Spectra Calibration under CHROMELEON
TM
Under CHROMELEON
TM
, spectra calibration is performed automatically after each "Lamp
on" or "Connect" command ("detector calibration"). The command "CheckWavelength"
allows you to include the largest wavelength deviation of this calibration in the Audit Trail. A
calibration is possible only when certain conditions are met:
•
During calibration, the baseline must be sufficiently stable. This may not be the case e.g.
when the solvent composition was modified or when there were air bubbles in the solvent.
•
The solvent in the cell must not be fully absorbing in the wavelength range which shall be
calibrated. This will be the case e.g. if the cell is filled with 96% hexane / 4 % ethyl
acetate.
•
Ensure for the calibration that the deuterium lamp is already warm because its spectrum
changes much during the first minutes after switching on the lamp.
If these conditions are not met, the process will be interrupted with the corresponding error
message. When the problem is solved, repeat the calibration using the command "Disconnect"
first followed by "Connect.
To calibrate the detector, the transmission spectrum of the deuterium lamp is compared with
that of the holmium oxide filter. With the resulting spectrum, the maxima are determined and
compared with the holmium oxide values stated in the literature. If, for a maximum, a
difference is detected between the measured and the known value, an interpolation is
performed between this maximum and the two adjacent maxima to correct the wavelength
allocation of the affected photodiodes. The spectra calibration can take up to 2 minutes.
During this time, data acquisition is not possible.
